I have no idea how it works since I don't own a copy of this game, but from what I've read of the facebook comments in the source link, you use the QR code scanner feature within the game to scan this and it gives you a (I assume) playable Blue Yoshi character.

I have no idea if that's new or not, but it was pretty much confirmed with screenshots that those costumes would be in the game. The Blue Yoshi only happened because of the fans voting for that colored Yoshi.

EDIT: Meant to say that those costumes would be available for the game, not that they're already in it.